The invention relates to an actuator with an electrically heatable thermostatic operating element mounted on a stationary body member and actuated by a heating element to move an operating piston that is in engagement with a motion transfer member that is biased by a compression spring, with the actuator having a housing that encloses the thermostatic operating element, the operating piston, the heating element, the motion transfer member, and the compression spring.
An actuator of this type is known, for example in U.S. Pat. No. 5,897,055 (German Patent Disclosure DE 197 05 721 A1). In that construction, it is not possible to detect the position of the actuator or to perform any function monitoring, without dismantling the outer housing.
In some actuators of this general type, an indicating element is provided that projects through the housing and is manipulated by an element of the actuator that moves with the operating piston so that the indicating element provides a visible indication of the position of the actuator exteriorly of the housing. This design requires an opening in the housing, with the risk of leakage. Moreover, additional parts are necessary to incorporate this feature.
It is the object of the present invention to provide an actuator with a simple way of monitoring the operating position of the components of the actuator. This object is attained by forming the outer housing at least partly of transparent material.
By the present invention, it is possible to observe one or more of the elements that move along with the operating piston of the thermostatic operating element, so that functional monitoring can be done in a simple way and the position of the actuator can be detected. The transparent material can be as clear as glass. However, even a milky to cloudy transparency suffices, since even then, motions and/or positions of components can still be readily detected. The particular advantage then is that no openings or the like through which moisture and/or contaminants could penetrate have to be provided in the outer housing.
In a specific embodiment of the invention, the transparent material is formed on a window in the housing, located where a component that moves with the operating piston can be viewed through the window. Such a window suffices to permit effective functional monitoring and/or the indication or display of the function.
Further characteristics and advantage of the invention will become apparent from the following description of the exemplary embodiment shown in the drawing.